National Timber Bridge Design Entry

College & Team Information
College or University:		Student Chapter:
Address:
Phone:	Fax:	E-mail:
Website address:		Faculty Advisor:
Person In Charge of Project:

Team Member	Class	Team Member	Class










Hours spent on project:		Cost of Material ($ Amount)
Student:	Faculty:	Donated:	Purchased:

1. Abstract - (Max 500 word narrative)
	The design concept was based on minimum deflection under maximum loading along with simplicity of design. To achieve simplicity of design and construction, along with weight minimization the truss originally planned was eliminated. A major component of the design concept was redundancy. Through the use of multiple members in both tension and compression, deflection was minimized. The challenge with this component was minimizing weight simultaneously. In order to achieve these goals the deck consists of 1x4 inch boards supporting a tongue and groove platform. The tongue and groove was both nailed and glued in order to force the deck to move as one piece, thereby maximizing stiffness. Another method of maximizing stiffness was the use of two 1x4 boards placed together to form a 2x4 which is also a compression component in the deck. A series of diaphragms also help to minimize deflection. Steel cable assemblies were used as a lightweight source to limit the tension in the bridge. The 1x12 boards running the length of the bridge were used to increase the moment of inertia in the side beams.

2. Deflection Table
Deflection (millimeters - rounded to 2 decimal places)
Loading Inc.	Bridge	Beam L	Beam R	Average (L&R)	Gross Deck	Net Deck
5 kN
10 kN
15 kN
20 kN - 0 min.
20 kN - 15 min.
20 kN - 30 min.
20 kN - 45 min.
20 kN - 60 min.
1) Loading Increments.
2) Bridge - As measured at midspan of the longitudinal beam receiving greatest loading.
3) Beam L - As measured under the longitudinal beam to left of selected deck monitoring point.
4) Beam R - As measured under the longitudinal beam to right of selected deck monitoring point.
5) Average (L&R) - Average of 3 and 4.
6) Gross Deck - As measured under the loading point expected to experience maximum deflection.
7) Net Deck - Column 6 minus column 5.
Deck span (transverse distance between main longitudinal bridge support members measured from inside edge to inside edge) = mm / 100 = mm (max. allowable net deck deflection)

3. Materials List
Material Item	Weight (kg)




















Total Weight (Kg)
Weight Non-wood (Kg)
Percent Non-wood

4. Summary -Describe Bridge and behavior under load - (Max 500 words)
	To measure deflection on our bridge, we loaded the bridge with 5 kN, 10 kN, and 15 kN. Next, a 20 kN load was applied for an hour and deflections were measured at fifteen minute intervals. The bridge was loaded twice to determine deflections. The loadings and times were recorded by videotape. The maximum average deflection of the bridge at various places was about seven millimeters. The bridge behaved well under the loading and produced no failures. From the results of the deflection measurements, the bridge deflected the most when loaded with the 5 kN load and the 10 kN load. Once the 20 kN load was added, the deflection did not change with time. The maximum deflection on each side for the beams and for the deck was approximately 0.3 inches (7.62 millimeters). For each loading at each place deflection was measured, the left beam, right beam, and deck, the deflection at 5 kN was close to 2.3 millimeters. The deflections for the 10 kN load were about 3.8 millimeters and the deflections at the 15 kN load were approximately 5.5 millimeters. The deflections measured for the deck loading and on each side of the beam corresponded with each other. The left and right beam deflections were slightly different. The left beam deflected 1.9 millimeters (0.75 in) under 5 kN of loading, while the right beam deflected 1.3 millimeters (0.51 in). Under 10 kN, the left beam deflected 3.6 millimeters (0.142 in) and the right beam deflected 2.5 millimeters (0.1 in). Also, under 15 kN, the left beam�s deflection was 5.6 (0.22 in) millimeters and the right beam�s deflection was 3.9 millimeters (0.154 in). Therefore, the left beam deflected slightly more than the right beam under each loading. Once the load was held constant for an hour, the left beam had a constant deflection of 8.6 millimeters and the right beam had a constant deflection of 6.1 millimeters. This could be caused from impurities in the timber used or slight error in equal lengths that could have a slight affect on the symmetry of the bridge. The net bridge deflection was 0.508 mm (0.020 in). This is below the calculated value our minimum bridge deflection which was 0.540 mm (.021 in). This is well beneath the 10 mm (0.393 in) value that would be the calculated maximum deflection value if this value was calculated by the stated rules. We chose to calculate our deflection to the much higher standard that would be considered good engineering design.

5. Project Drawings and Photos

Longitudinal Cross Section	Tranverse Cross Section	Trimetric View	Project Photo	Team Photo
Click on drawing or photo above for larger view.

6. Component Details
In ten (10) words or less per each component below, describe the bridge:
Stringers/Girders:	Girders consist of a laminated 1x12, 1x6, and 1x4.
Deck:	The deck is made of 4 in. tongue and groove.
Floor Beams:	The floor beams consist of 2x4 boards.
Suspension:
Unique:	Steel cables were used to provide tension support.

Describe preservative treatment for all wood members. Include type and concentrations. Also include a short statement of why this treatment was selected. Did the treatment requirement present any special problems? If yes, provide details
	All members were treated to 0.40 pcf, LP 2z, bromated copper and arsenate standards. Retention is the amount of preservative retained in the wood and is measured in pounds per cubic foot (pcf). This treatment method was selected based on two major components. It is a common treatment for the kind of lumber used for the job, and it will withstand normal loading conditions.

7. Special Considerations
	After the excellent performance that was achieved by this design, we felt it would be a waste to simply destroy it. Instead it will be put to use as an ATV bridge in a wooded area.